Transmission assembly

ABSTRACT

A compact hydraulic transmission assembly using an axial piston pump disposed on a center section that also provides a cylindrical running surface for a radial piston motor. This design provides for a compact and low profile assembly, while the combination of an axial piston pump with a radial piston motor provides improved efficiency for higher torque output. The radial piston motor includes a lower mass piston block that improves performance. The center section includes an extension extending outwardly from its circumference and including a check port; and a mounting lobe for securing the center section is secured to the pump housing.

CROSS REFERENCE

This application is a continuation of U.S. patent application Ser. No.14/484,559, filed on Sep. 12, 2014, which claims the benefit of U.S.Provisional Patent Application 61/876,905, filed Sep. 12, 2013, which isincorporated herein in its entirety.

BACKGROUND OF THE INVENTION

This invention relates to hydraulic pumps and motors used to transmitrotational force from a prime mover to an output. Such devices may beused in applications including but not limited to zero-turn mowers, fandrives and the like.

SUMMARY OF THE INVENTION

This invention discloses a compact hydraulic transmission assembly usingan axial piston pump disposed on a center section that also provides acylindrical running surface for a radial piston motor. This designprovides for a compact and low profile assembly, while the combinationof an axial piston pump with a radial piston motor provides improvedefficiency for higher torque output. The radial piston motor includes alower mass piston block that improves performance.

A better understanding of the invention will be obtained from thefollowing detailed descriptions and accompanying drawings, which setforth illustrative embodiments that are indicative of the various waysin which the principals of the invention may be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a transmission assembly in accordancewith the principles disclosed herein.

FIG. 2 is a perspective view similar to FIG. 1 with the pump housingremoved.

FIG. 3 is a perspective view similar to FIG. 2 with certain internalcomponents removed to further illustrate additional structure.

FIG. 4 is a top plan view of the internal assembly as shown in FIG. 3.

FIG. 5 is a sectional view along the line 5-5 in FIG. 4.

FIG. 6 is a perspective view of certain internal components of thetransmission assembly.

FIG. 7 is a perspective view of the motor housing along with certaincomponents of the transmission assembly.

FIG. 8 is a top plan view of the motor housing and certain componentsshown in FIG. 7.

FIG. 9 is a top perspective view of the radial piston motor and outputshaft.

FIG. 10 is a bottom perspective view of the radial piston motor andoutput shaft of FIG. 9.

FIG. 11 is an exploded bottom perspective view of certain components ofthe transmission assembly.

FIG. 12 is a top plan view of the center section of the transmissionassembly.

FIG. 13 is a side elevational view of the center section of FIG. 12.

DETAILED DESCRIPTION OF THE DRAWINGS

The description that follows describes, illustrates and exemplifies oneor more embodiments of the invention in accordance with its principles.This description is not provided to limit the invention to theembodiment(s) described herein, but rather to explain and teach theprinciples of the invention in order to enable one of ordinary skill inthe art to understand these principles and, with that understanding, beable to apply them to practice not only the embodiment(s) describedherein, but also any other embodiment that may come to mind inaccordance with these principles. The scope of the invention is intendedto cover all such embodiments that may fall within the scope of theappended claims, either literally or under the doctrine of equivalents.

It should be noted that in the description and drawings, like orsubstantially similar elements may be labeled with the same referencenumerals. However, sometimes these elements may be labeled withdiffering numbers or serial numbers in cases where such labelingfacilitates a more clear description. Additionally, the drawings setforth herein are not necessarily drawn to scale, and in some instancesproportions may have been exaggerated to more clearly depict certainfeatures. As stated above, this specification is intended to be taken asa whole and interpreted in accordance with the principles of theinvention as taught herein and understood by one of ordinary skill inthe art. The use of various fasteners depicted herein is illustrativeonly and it will be understood by those of skill in the art that othermeans of securing the components could be alternatively used.

Transmission assembly 20 comprises a first portion, or pump housing 23,secured to a second portion, or motor housing 24, by means of a seriesof fasteners 25 to form an internal sump 29 in which center section 50is secured by a series of fasteners 51. Center section 50 includes aplurality of mounting lobes 50 r that extend outwardly therefrom toreceive fasteners 51. Transmission assembly 20 may be connected to anexternal expansion tank (not shown) by means of a port (not shown)formed on an external surface thereof.

Pump 30 comprises a rotatable cylinder block 31 disposed on a pumprunning surface 50 a, and a plurality of pump pistons 32 are disposed incylinder block 31 in a known manner. Pump input shaft 21 extends intopump housing 23 through support bearing 22 to engage and rotatably drivecylinder block 31. Pump input shaft 21 has one end 21 a supported inbore 50 g formed in center section 50. Pump 30 also comprises a thrustbearing 33 disposed in a swash plate 34, which has a trunnion arm 35engaged thereto to rotate swash plate 34 and control output of pump 30in a known manner. Trunnion arm 35 extends out of pump housing 23.

Center section 50 has fluid porting formed therein comprising fluidpassages 50 c connecting pump ports 50 b on pump running surface 50 a tomotor ports 50 d, described in more detail below. A cylindrical motorrunning surface 50 q is formed on pintle 50 h that extends from thebottom of center section 50, as seen in, e.g., FIG. 11. The motor ports50 d are formed on running surface 50 q to hydraulically connect radialpiston motor 40 to fluid passages 50 c and thus to pump 30. Ribs 50 eprovide further structural support.

As seen in FIG. 12, the arrangement of mounting lobes 50 r around thecircumference of center section 50 in a “Y” shape provides for aparticularly compact design. Check plug ports 50 f are formed in anextension 50 t located between the two arms of the “Y” shape formed bylobes 50 r and act to connect fluid passages 50 c to sump 29. Checkplugs 52 are mounted in ports 50 f and are located on the top surface ofcenter section 50 (i.e., the same side as the pump running surface 50 a)to provide for a more compact unit. A rotary bypass 60 extends out ofthe pump housing 23 and enables the user to open the check plugs 52 toplace the unit into bypass mode.

Radial piston motor 40, as can be seen in FIGS. 7-11, comprises anoutput hub 47 that is press-fit into or otherwise mechanically engagedto a piston block 41 having a plurality of piston bores 41 a formedtherein to receive the respective pistons 42. This mechanical engagementresults in a sealed joint between hub 47 and piston block 41 to preventleakage of hydraulic fluid through this joint.

Piston block 41 has a series of enlarged areas 41 d formed to acceptpistons 42. Enlarged areas 41 d are connected by thinner webs 41 e toform an undulating profile that reduces material mass. This reduction inmaterial mass reduces cost and provides less running inertia.

Each piston 42 comprises a piston body 43 engaged to piston spring 45and having piston ball 44 disposed therein, where piston balls 44 engagerace surface 27 a of the piston race ring 27, which rides in motorhousing 24. As shown in, e.g., FIGS. 4 and 6, a plurality of lubricationgrooves 27 b may be formed in an external surface of piston race ring 27to cooperate with lubrication grooves 24 a formed in motor housing 24 topermit an oil film to develop between race ring 27 and motor housing 24if it is desired to have race ring 27 rotate. One may also use astandard bearing in place of race ring 27, and in such an embodimentstandard bull nose pistons could be used.

Motor output shaft 49 is driven by motor 40 and supported in motorhousing 24 by a bearing 48, and the internal end 49 a extends into andis supported by bore 50 i of center section 50. Output hub 47 has aflange portion 47 d and cylindrical structure 47 b extending therefromand extending into and supported by bore 41 b of the motor piston block41. Fluid openings 47 a are formed in hub 47 to permit fluidcommunication between fluid passages 50 c and piston bores 41 a as seenin, e.g., FIG. 11. A pressure relief passage 47 f is provided to permitfluid discharge to sump 29 to avoid pressure buildup below hub 47.

Flange portion 47 d includes a plurality of slots 47 c formed therein.Output hub 47 is aligned to piston block 41 by means of piston blocktabs 41 c engaged to slots 47 c as shown in, e.g., FIGS. 10 and 11. Inthe event of mechanical joint slippage, tabs 41 c engaged to slots 47 ccan maintain alignment of piston block 41 with hub 47 while driving hub47. Splines 47 e on hub 47 engage with splines 49 b on output shaft 49to transmit rotational force of motor piston block 41 to output shaft49.

Thrust washer 53 is disposed between motor piston block 41 and thebottom of center section 50 where it is supported by land 50 p.

Various pressure relief structures may be machined into center section50. For example, as shown in FIGS. 11 and 13, a pressure relief groove50 n is formed into the bottom surface of center section 50 and extendsonto adjacent pintle 50 h to intersect with low pressure groove 50 m.

Referring to FIG. 13, two high pressure grooves 50 j are provided onrunning surface 50 q, one above and one below the motor ports 50 d, tocreate a high pressure fluid band about pintle 50 h that causeshydrodynamic centering of radial piston motor 40 thereon. Additionally,a low pressure groove 50 m and a low pressure chamfer 50 k are formed,respectively, above and below the high pressure grooves 50 j to definethis high pressure fluid band and provide balance between radial pistonmotor 40 and pintle 50 h. Low pressure chamfer 50 k communicates withthe aforementioned pressure relief passage 47 f.

While specific embodiments of the invention have been described indetail, it will be appreciated by those skilled in the art that variousmodifications and alternatives to those details could be developed inlight of the overall teachings of the disclosure. Accordingly, theparticular arrangements disclosed are meant to be illustrative only andnot limiting as to the scope of the invention which is to be given thefull breadth of the appended claims and any equivalent thereof.

I claim:
 1. A transmission assembly comprising: a pump housing; and acenter section disposed in the pump housing, the center sectioncomprising: a running surface having a circumference; a mounting lobeextending outwardly from the circumference and having an openingsubstantially perpendicular to the running surface, the mounting lobeengaged with the pump housing; and an extension extending outwardly fromthe circumference and including a check plug port substantiallyperpendicular to the running surface.
 2. The transmission assembly ofclaim 1, wherein the mounting lobe is one of a plurality of mountinglobes engaged with the pump housing.
 3. The transmission assembly ofclaim 2, wherein the extension is disposed between two of the pluralityof mounting lobes.
 4. The transmission assembly of claim 2, wherein theplurality of mounting lobes are offset from one another in a “Y” shape.5. The transmission assembly of claim 1, further including a check plugin the check plug port.
 6. The transmission assembly of claim 5, furtherincluding a bypass shaft engaged with the check plug and extendingthrough the pump housing.
 7. The transmission assembly of claim 1,further including a motor housing engaged with the pump housing to forma common sump between the pump housing and the motor housing.
 8. Thetransmission assembly of claim 7, further including a motor shaftextending through the motor housing and supported by the center section.9. The transmission assembly of claim 1, wherein the center sectionincludes a low pressure chamfer.
 10. The transmission assembly of claim9, further including a radial piston motor rotatably engaged with thecenter section, the radial piston motor including a pressure reliefpassage in fluid communication with the low pressure chamfer.
 11. Atransmission assembly comprising: a pump housing; and a center sectionhaving a circumference, the center section further comprising: amounting lobe having an opening and extending radially from thecircumference; and an extension having a check port and extendingradially from the circumference; wherein the center section is securedin the pump housing via the mounting lobe and the check port issubstantially parallel to the opening.
 12. The transmission assembly ofclaim 11, wherein the mounting lobe is one of a plurality of mountinglobes offset from one another in a “Y” shape and the extension isdisposed between two of the plurality of mounting lobes.
 13. Thetransmission assembly of claim 11, further including a check plug in thecheck port and a bypass shaft engaged with the check plug and extendingthrough the pump housing.
 14. The transmission assembly of claim 11,further including a motor housing engaged with the pump housing to forma common sump between the pump housing and the motor housing.
 15. Thetransmission assembly of claim 14, further including a motor shaftextending through the motor housing and supported by the center section.16. The transmission assembly of claim 11, wherein the center sectionincludes a low pressure chamfer and further including a radial pistonmotor rotatably engaged with the center section, the radial piston motorincluding a pressure relief passage in fluid communication with the lowpressure chamfer.
 17. A center section for use in a transmissionassembly, the center section comprising: a running surface having acircumference; an extension extending outwardly from the circumferenceand including a check port; and a mounting lobe extending outwardly fromthe center section and having an opening substantially parallel to thecheck port, wherein the center section is secured in a pump housing viathe mounting lobe.
 18. The center section of claim 17, wherein themounting lobe is one of a plurality of mounting lobes offset from oneanother in a “Y” shape and the extension is disposed between two of theplurality of mounting lobes.
 19. The center section of claim 17, furtherincluding a motor housing engaged with the pump housing to form a commonsump between the pump housing and the motor housing.
 20. The centersection of claim 19, further including a motor shaft extending throughthe motor housing and supported by the center section.